Tricyclic antidepressants inhibit voltage-dependent calcium channels and Na(+)-Ca2+ exchange in rat brain cortex synaptosomes.
We have used a resting (5 mM K+) or depolarizing (60 mM K+) choline-based medium, and a nondepolarizing sodium-based or choline-based medium, to characterize the inhibitory potential of tricyclic antidepressants against the voltage-dependent calcium channels or the Na(+)-Ca2+ exchange process, respectively, in synaptosomes from rat brain cortex. Imipramine, desipramine, amitriptyline, and clomipramine inhibited net K(+)-induced 45Ca uptake with similar IC50 values (26-31 microM), and this uptake was also inhibited by diltiazem with an IC50 of 36 microM; these results indicate an inhibition of voltage-dependent calcium channels by tricyclic antidepressants. The net uptake of 45Ca induced by Na(+)-Ca2+ exchange was also inhibited by the four tricyclic antidepressants tested, but not by diltiazem; imipramine (IC50 = 94 microM) was a more potent inhibitor of this process than desipramine (IC50 = 151 microM), and the IC50 values of amitriptyline (107 microM) and clomipramine (97 microM) were similar to that of imipramine. Some degree (approximately 25%) of brain calcium channel blockade could be present at the steady-state concentrations of tricyclic antidepressants expected to occur therapeutic use of these compounds to treat depression or panic disorder.
Lavoie
P A
PA
Département de pharmacologie, Université de Montréal, Québec, Canada.
Beauchamp
G
G
Elie
R
R
D000818:Animals; D000929:Antidepressive Agents, Tricyclic / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers; D002132:Calcium Radioisotopes; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D002794:Choline / Q000494:pharmacology; D004110:Diltiazem / Q000494:pharmacology; D066298:In Vitro Techniques; D007474:Ion Exchange; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*
D000929:Antidepressive Agents, Tricyclic; D002121:Calcium Channel Blockers; D002132:Calcium Radioisotopes; D012964:Sodium; D004110:Diltiazem; D002794:Choline; D002118:Calcium